This invention relates to the generation of radiographs, including cardiac and non-cardiac angiographs. More particularly, this invention relates to a method and apparatus for generating a non-cardiac angiograph on a cardiac angiography system.
A radiograph is an image produced by the emissions, typically X-rays, from a radioactive substance. An angiograph is a radiograph generated by capturing an X-ray image after injecting a radiopaque substance. Cardiac angiography refers to the imaging of the heart, whereas non-cardiac angiography refers to the imaging of other organs and arteries. Cardiac and non-cardiac X-ray images are used for viewing the flow of blood in the heart or other organs and body parts. Because the heart moves rapidly during an examination, many frames of short duration are captured so as to view the dynamic motion of the heart in a group of clear focused images. Because other organs move relatively slow or not at all compared to the heart, fewer frames of longer duration may be captured, while still obtaining clear focused images.
For a conventional cardiac exam implemented with a cardiac angiography system, X-rays are emitted toward a subject. Some of the X-rays are absorbed or scattered, while other X-rays pass through the subject toward an image intensifier. The passed X-rays are converted by the image intensifier to an optical image which, through the use of mirrors and/or beam splitters, is focused at either or both of a film camera (i.e., 35 mm) and a TV camera. The film camera is used for capturing multiple still shots for exposure as individual photographs. The TV camera is used for capturing multiple shots which are converted into digital video image samples, then processed and combined to form a dynamic video image sequence.
For a conventional non-cardiac exam implemented with a non-cardiac angiography system, the functional operation is similar to that as described for the cardiac angiography system. A film camera may be used to capture one or more still photographs, while a TV camera may be used to capture and format a dynamic video image sequence.
For a typical cardiac exam, approximately ten sequences of images may be obtained so as to view the heart at different projections. A single sequence lasts approximately 8 seconds and is formed by a plurality of frames captured generally at a rate of 30 or 60 frames per second (fps), and sometimes at rates as high as 90 fps or 150 fps. Each frame within a sequence is formed by transmitting an X-ray pulse of approximately 2 to 10 milliseconds and capturing the resulting radiograph on the 35 mm film and/or TV camera. For each X-ray pulse of 2 to 10 milliseconds, an X-ray exposure of approximately 20 to 100 micro-Roentgens is achieved as measured at an image intensifier input surface.
For a typical non-cardiac exam, the number and length of sequences may vary. In addition, the number of frames that may form a sequence may vary. Compared to the sequence for a cardiac exam, the sequence for a non-cardiac exam is formed by a plurality of frames captured at a slower rate, such as 1-8 frames per second (fps). In addition, the typical non-cardiac application requires a larger exposure level (i.e., approximately 1000 micro-Roentgens as measured at the surface of the image intensifier). Such exposure level may be achieved with an X-ray pulse of longer duration (i.e., 50 to 100 milliseconds).
The cardiac exam requires shorter pulses and more frames so as to capture the faster motion of the heart in a focused non-blurred image sequence as previously discussed. Such short pulses typically limit the exposure level that can be used for a cardiac exam. For the non-cardiac exam fewer frames and approximately the same number of sequences are needed. Thus a larger exposure level may be used to enhance the quality of the formed image and thereby enable smaller and/or low contrast objects to b discerned.
The differing requirements (e.g., exposure level, exposure duration, frames per second) for acquisition of cardiac and non-cardiac exams result in differences in the systems upon which these exams are performed. A conventional system which supports both types of exams is costlier than a system which only supports one type of exam. Accordingly, a more efficient solution is needed for achieving non-cardiac exams on a system which normally is used for acquiring only cardiac exams.